The invention concerns a disc brake for vehicles, in particular for commercial vehicles, with brake pads which are arranged on both sides of a brake disc, with a brake application device for applying one of the brake pads on an application side, and with a brake caliper for transferring the application force to the brake pad on the other side, i.e. the reaction side, of the brake disc.
Brake calipers of pneumatically activated disc brakes for heavy goods vehicles are normally produced as castings because of the freedom of design and ease of production. The material used is cast iron with spheroidal graphite in a high strength class.
A generic disc brake is shown in DE 37 16 202. The disc brake disclosed in this publication is activated pneumatically and therefore suitable above all for use in the commercial vehicle sector, where it has also proved successful in practice. A brake caliper made of cast iron is used as a force transmission device to transmit the application force to the brake pad on the reaction side.
These brake constructions, like all axle components of commercial vehicles, face continuous demand to have their weight reduced, since a reduction in weight firstly increases the possible payload, but secondly the reduction in the unsprung mass of the axle components also contributes to protecting the load and improving the driving qualities and hence traffic safety. Weight optimization of the brakes has progressed so far that no further improvement appears possible with the casting materials available without an increased risk of fracture of the brake caliper and/or increased deformation thereof, with the consequence of a deterioration in operating behavior (stroke, response time, compressed air consumption, uneven pad wear, etc.).
Steel appears suitable as an alternative material since very high strength can be achieved, combined with a high elongation at failure and hence a high fatigue strength. And, the around 35% higher modulus of elasticity of steel under the same stress, in comparison with the cast-iron materials previously used, guarantees a low deformation of the caliper. To achieve the desired low weight with low production cost, the use of sheet steel appears suitable. An initial approach for producing a sheet steel caliper as a composite construction is described in DE 196 42 384 A1.
DE 196 42 384 A1 proposes a compressed-air actuated disc brake, the force transmission device of which, to transmit the application force to the brake pad on the reaction side i.e. of the brake caliper, is configured in the manner of a fully closed frame which absorbs the application forces. A modular body holds the brake mechanism and allows pre-assembly. The closed frame is produced from sheet metal in a forming process.
A more extensive, solid sheet steel construction of the brake caliper is not competitive in relation to costing structure, since the waste from the semifinished metal product used has a clearly negative effect on the cost structure of a brake caliper made of sheet steel. The high material cost proportion results substantially from the complex geometry of the brake caliper frame, which necessarily gives a higher waste proportion in a solid sheet steel construction.
The prime development objective however remains an optimization of weight and cost of the disc brake. Because of the dominant weight component, and hence its dominance with regard to the cost structure of a disc brake, attention is focused in particular on the brake caliper for weight and cost reduction. A reduced weight of the brake caliper has a significant effect in reducing the unladen weight, which is an important aspect in particular in commercial vehicle brakes, since a low vehicle unladen weight allows a higher payload.
In addition, due to the lower weight of the brake caliper, the unsprung weight on the vehicle is reduced, which has a positive effect on the agility of the vehicle and on the driving comfort, which, for example, is another important aspect in particular in cars but also in coaches.
The invention is therefore based on the object of creating a disc brake which avoids said disadvantages and which can be produced cost-effectively and hence economically, and which has a significant weight and cost advantage in relation to a disc brake with a one-piece cast brake caliper.
The invention achieves this object in that it creates a disc brake with a brake caliper which, on the reaction side, has a caliper frame made of a formed hollow steel profile to transmit the application force to the brake pad.
This brake caliper frame is now connected by welding with a caliper head produced, for example, as a deep-drawn sheet metal part, but a combination with a cast caliper head is also possible.
With this production method, the material loss is reduced to a minimum. In production of the hollow steel profile, only trimming of the edges is required. The caliper head produced, for example, from sheet metal is a trough-like deep-drawn part which can also be produced without great waste. The necessary welding operations are reduced to connecting the caliper frame to the caliper head.
The U-shaped caliper frame is formed from a hollow profile, wherein the form is greatly determined by the brake disc, the outboard brake pad and the rim and wheel hub rotating about the wheel brake. The smaller the distance from the rotating parts of the wheel, the more construction space is available for the brake, to achieve higher braking performance.
For this reason, the construction space available for the caliper frame is very limited. The lateral tension struts of the caliper frame, which transmit the application force of the brake to the rear, must be located in the annular gap between the brake disc and the wheel rim and offer sufficient clearance to absorb production tolerances, thermal expansion of the brake disc and load-induced deformation. The rear of the caliper frame, via which the reaction force transmitted from the tension struts is introduced into the outboard brake pad, requires a high bending strength, since this feature substantially determines the caliper deformation. Secondly, the axial construction space required by the caliper rear must be as small as possible so that in its installation position, the brake disc can be moved as far as possible to the outside in order to achieve a favorable steering radius.
The result of these peripheral conditions is that the tension struts are constructed very flat in the radial direction and bridge the brake disc relatively widely in order to achieve the necessary cross-section for transmission of the tensile force. In contrast, to achieve a maximum possible bending strength in the axial direction, the caliper rear is constructed as thick as possible, whereby an approximately square cross-section results.
With a caliper frame made from a hollow profile, the problem now exists of configuring these totally different cross-section shapes and dimensioning requirements from a piece of tube with constant diameter and wall thickness. A requirement for forming is, for example, that the length of the peripheral neutral fibers in each cross-section must necessarily be equal to the length of the circumference line on the center diameter of the tube.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.